This article reports 13 cases of pneumococcal septic arthritis and reviews another 177 cases reported since 1965. Of 2407 cases of septic arthritis from large series, 156 (6%) were caused by Streptococcus pneumoniae. Mortality was 19% among adults and 0% among children. Pneumococcal bacteremia was the strongest predictor of mortality. At least 1 knee was involved in 56% of adults. Polyarticular disease (36%) and bacteremia (72%) were more common among adults with septic arthritis caused by S. pneumoniae than among adults with other causative organisms. Only 50% of adults with pneumococcal septic arthritis had another focus of pneumococcal infection, such as pneumonia. Functional outcomes were good in 95% of patients. Uncomplicated pneumococcal septic arthritis can be managed with arthrocentesis and 4 weeks of antibiotic therapy; most cases of pneumococcal prosthetic joint infection can be managed without prosthesis removal. A fatal case of septic arthritis caused by a b-lactam-resistant strain of S. pneumoniae is also presented.Pneumococcal septic arthritis is described as "rarely encountered" [1] or "unusual" [2]. However, Streptococcus pneumoniae causes septic arthritis more often than is generally thought. Ispahani et al.[3] last reviewed pneumococcal septic arthritis in this journal, reporting 32 cases and reviewing 58 cases from large series published since 1965. We present 13 previously unreported cases and review 177 cases of pneumococcal septic arthritis reported in the English-language literature since 1965 , emphasizing the frequency of bacteremia and polyarticular disease among adults, the absence of extra-articular infection in many patients, and the emerging problem of pneumococcal antibiotic resistance. We report 2 cases of pneumococcal prosthetic joint infection and a case of pneumococcal arthritis in an adult that was caused by a strain of S.